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The 1400-MW Kii-Channel HVDC System

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					                                                                                  The 1,400-MW Kii-Channel HVDC System   114

The 1,400-MW Kii-Channel HVDC System



Hiroyuki Nakao                           OVERVIEW: High-voltage direct current (HVDC) transmission systems are
Masahiro Hirose                          widely used in many projects all over the world. In Japan, several HVDC
                                         systems are in operation, and a new system, the Kii-Channel HVDC, was
Takehisa Sakai
                                         put into operation in June, 2000. The HVDC is a bulk transmission system
Naoki Kawamura                           and its transmission capacity is to be built up to 2,800 MW. Hitachi supplied
Hiroaki Miyata                           the main equipment for this system, such as thyristor valves, converter
Makoto Kadowaki                          transformers, and control & protection panels. These products are based
Takahiro Oomori                          on state-of-the-art technologies described below.
Akihiko Watanabe




INTRODUCTION                                                        The Kii-Channel HVDC system constructed by the
HIGH-voltage direct current (HVDC) transmission                  Kansai Electric Power Co., Inc., the Shikoku Electric
systems (including frequency-conversion systems and              Power Co., Inc., and the Electric Power Development
submarine DC-link and non-synchronous                            Co., Ltd., has been in commercial operation since July,
interconnection systems) are used in many projects               2000. Hitachi supplied the main equipment for the
all over the world. HVDC systems feature easy power-             pole-II terminals of the project. In this article, we
flow control, stable cable transmission, and                     describe the project features and new technologies.
economical operation for long-distance transmission.
The capacities of some of these systems exceed 3,000             HVDC SYSTEM
MW. In Japan, 50/60-Hz frequency-converter systems                  The Kii-Channel HVDC system is the first bulk
are more common than other systems. A DC submarine               HVDC transmission system and the largest HVDC
cable transmission system is also used between                   system in Japan, which is to transmit power from the
Honshu and Hokkaido as well as for non-synchronous               Anan converter station in Shikoku to the Kihoku
interconnection between the Hokuriku Electric Power              converter station in Honshu via the Yura switching
System and the Chubu Electric Power System. Before               station through an approximately 50-km-long
the beginning of 2000, the capacity of these systems             submarine cable and an approximately 50-km-long
ranged from 300 to 600 MW and was 1,800 MW in                    overhead transmission line to send part of the power
total.                                                           from the Tachibana-bay thermal power plant (the total




Fig. 1— Terminals of the Kii-Channel
       HVDC System: Anan Converter
Station and Kihoku Converter Station.
 The Anan converter station is located
in a seaside area near the Tachibana-
  bay thermal power plant in Shikoku.
       The Kihoku converter station is
 located in an inland area in Honshu.
   Both terminals are connected by an
approximately 50-km-long submarine
   cable and an approximately 50-km-              Anan converter station                Kihoku converter station
               long transmission line.
                                                                                                                     Hitachi Review Vol. 50 (2001), No. 3      115

generation capacity is 2,800 MW) (see Fig. 1). This                                   converter transformers, and system control and
system is of the largest class in the world. It was put                               protection panels for the pole-II terminals. In addition,
into commercial operation as the Kii-Channel HVDC                                     for the Kihoku converter station, Hitachi also supplied
project, Phase I (1,400 MW, DC±250 kV, 2,800 A), in                                   a substation control system (SCS). The main features
June, 2000. A one-line diagram of the HVDC system                                     of the Kii-Channel HVDC system are listed in Table
is shown in Fig. 2.                                                                   2, which shows such advantages of the HVDC system
    The specifications of the main equipment of this                                  as its high-speed power-flow control.
HVDC project are listed in Table 1. Hitachi supplied                                      The system has a DC continuous operation function
the main equipment including thyristor valves,                                        during AC-system faults to ensure the power system




                                                            Compensation             Direct-current reactor
                                                            transformer



                                                                                                                           DCF
                                                                    ACF
                                                                                     Thyristor
                                                       SC                            valve
                                                                                                                           MRTB
                                                                   Converter
                                                                   transformer                                                   NCB




                                                                                                 Cable    Overhead
Fig. 2— Main Circuit Diagram of the                         Anan converter station                        line                  Kihoku converter station
        Kii-Channel HVDC, Phase I.                                                           Yura switching station
1,400-MW transmission with bipolar                 ACF: alternating-current filter     NCB: neutral-line circuit breaker                : phase II (±500 kV)
  metallic return 700-MW × 2 HVDC                  SC: static condenser                MRTB: metallic return transfer breaker
                                                   DCF: direct-current filter
                           systems.




TABLE 1. Specifications of the Main Equipment of the Terminals                        TABLE 2. Characteristics and Main Functions of Kii-Channel
(Kii-Channel HVDC, Phase I)                                                           HVDC System
                     Anan converter station       Kihoku converter station              Characteristics       Purpose/duty                    Function
 Thyristor           DC 250 kV, 700 MW             DC 250 kV, 700 MW                                                               • Continuous operation during
 valve              (125% over-load) × 2 pole     (125% over-load) × 2 pole                                                          AC-system faults
                                                                                        Bulk power
 Converter              500/110/110 kV,               500/110/110 kV,                                     • High reliability       • High-speed power recovery
                                                                                        transmission
 transformer           872 MVA × 2 pole              872 MVA × 2 pole                                                              • Over-load operation for
                                                                                                                                     power-system emergencies
 Compensation            500/60/66 kV,                  500/71 kV,
 transformer           270 MVA × 2 pole              450 MVA × 2 pole                   AC-DC                                      • Power modulation (PM)
                                                                                        hybrid power • Transient power-            • Emergency frequency
 Shunt                  66 kV, 120 MVA               77 kV, 120 MVA                                    system stability
                                                                                        transmission                                 control (EPPS, EFC)
 capacitor                  × 4 group                    × 6 group
 Harmonic              500 kV, 270 MVA               500 kV, 270 MVA                                                               • Generator-frequency control
 filter               (5th, 11th, 13th, HP)         (5th, 11th, 13th, HP)                                                            (EPPS, EFC)
                                                                                        Isolated          • Cooperative
                                                                                                                                   • Supplemental subsynchronous
                       DC 500-kV reactor            DC 500-kV reactor                   power               control with
 DC switch                                                                                                                           damping control (SSDC)
                           DC-GIS                     MRTB, NCB                         generation          generator
                                                                                                                                   • Higher harmonic/overvoltage
                                                   500-kV air-insulated                                                              control
 AC switch                 500-kV GIS
                                                         + GIS
                                                                                                          • High reliability
HP: high pass                                                                           Flexible          • Easy operation   • Redundant system
DC-GIS: direct current gas-insulated switchgear                                         operation         • Easy maintenance

                                                                                        EPPS: emergency power presetter    EFC: emergency frequency control
                                                                                        SSDC: supplemental subsynchronous damping controller PM: power modulation
                                                                                  The 1,400-MW Kii-Channel HVDC System        116


     AC line voltage at
     inverter terminal
              (phase A)



              (phase B)



              (phase C)


     DC voltage
                          0
                              -250 V

     DC current               2,800 A
                          0                                                                            Fig. 3— Results of
                                                                                                       Continuous Operation.
                                                                                                       Although the system
     Delay angle α
     of inverter                                                                                       voltage drops due to a
                          0                                                                            fault in the AC system,
                                                                                                       the power is recovered
     Extinction angle γ                                                                                quickly after the fault
     of inverter
                          0                                                                            without commutation
                                                                                                       failure.




stability. This function is based on a new method to
minimize the chance of commutation failure. In                Without PM        65.0
                                                                                                      Generator phase angle
systems with conventional control, operation stops                                        A
when the AC voltage drops to avoid commutation                                                         C
                                                                  (Degrees) 22.5
failure, but in this system, transmission control                                                      D
continues during an AC-system fault as a result of new
                                                                                -20.0
control methods developed for quick detection of                                    0.0                                  15.0
extinction angles, harmonic voltages, and AC transient                           1.3
voltages. These methods enable the power system to                 (Per unit)                                    DC power
be stabler than that in systems with conventional                                0.0
                                                                                   0.0                                   15.0
control (see Fig. 3).
   This function was found effective during AC-               With PM           65.0
                                                                                                  A        Λ=0.81   Θ=0.97
system faults due to a lightening impulse.
   Power modulation is a technology used to stabilize                                      C               Λ=0.46   Θ=0.65
                                                                  (Degrees) 22.5
AC power with DC power modulation against power                                               D       Generator phase angle
fluctuation due to an AC-system fault (see Fig. 4). The
                                                                                -20.0
power flow of the HVDC system is additionally                                       0.0                                  15.0
controlled against power fluctuation, which is detected                          1.3
by measuring the frequency deviation of the terminals.             (Per unit)                                    DC power
This function was tested before the system was put                               0.0
                                                                                   0.0                                   15.0
into commercial operation and its effectiveness against                                               Time (s)
power fluctuation was verified.                               PM: power modulation

   The new technologies described above were
                                                          Fig. 4— Simulation of Power-Flow Damping.
developed as a result of a system study and simulation    The graphs show power fluctuation in system generators A, C,
and they are based on Hitachi’s experience as a leader    and D at the time of a 3-line ground fault/open circuit in a 60-
in power transmission and distribution field.             Hz system. Power fluctuation is damped by DC power control.
                                                          Damping effect is larger for smaller values of indexes Λ and Θ.
                                                                                                   Hitachi Review Vol. 50 (2001), No. 3   117

THYRISTOR VALVE                                                          (3) valve structure designed based on a simulation
    Thyristor valves are the main pieces of equipment                    technology for seismic conditions.
in HVDC power transmission systems. They convert                             The number of thyristors connected in a series was
AC/DC voltages. The thyristor valves in the Kii-                         reduced due to the use of high-voltage thyristors
Channel HVDC system are water-cooled and air-                            developed for this project, which resulted in compact
insulated, with direct-light-triggered thyristors that                   thyristor valves. The thyristor valves have a quadruple
were used in several other HVDC projects in Japan                        multi-valve structure. A model test was conducted to
(see Table 3).                                                           evaluate the performance of the valves and new
    To reduce the loss of the thyristor valves and                       structures including supporting frames, under seismic-
minimize their size for the Kii-Channel HVDC project,                    event conditions. The thyristor valves in this project
Phase II, a 500-kV, 2,800-MW system (1,400 MW per                        are 0.87 times higher and their volume density is 0.5
pole) and newly designed thyristor valves were used                      times greater compared to the height and volume
in this project (see Fig. 5). The new design has the                     density of conventional valves (see Fig. 6).
following elements;                                                          The coolant used for primary heat exchange in the
(1) compact thyristor-valve module with 8-kV, 3,500-                     thyristor valves is deionized water. At the Kihoku
A direct-light-triggered thyristors;                                     converter station located in the highlands with a limited
(2) compact thyristor valves with dimensions tested                      supply of cooling water, the cooling system is a
through field and model experiments;                                     combination of air coolers and water coolers. New




TABLE 3. Performance of Thyristor Valves for Kii-Channel
HVDC, Phase I
   Capacity                          700 MW

 DC voltage     250 kV

 DC current     2,800 A (3,500 A-30 min. over-load)

 Main devices   8-kV, 3,500-A direct-light-triggered thyristor (LTT’s)

 Insulation     Air-insulated

 Cooling        Deionized water

 Structure      Quadruple multi-valve unit (MVU)

 Dimension      5.2 m × 3.8 m × 9.5 m




                                                                         Fig. 6— A 700-MW Quadruple Multi-Valve Unit.
Fig. 5— Thyristor-Valve Module.                                          The size per unit of electrical capacity was reduced to 60% of
Compact thyristor-valve module with 8-kV, 3,500-A direct-light-          that of a conventional thyristor valve with 8-kV, 3,500-A direct-
triggered thyristors.                                                    light-triggered thyristors.
                                                                                 The 1,400-MW Kii-Channel HVDC System     118

methods to control the loss of the thyristor valves and     TABLE 4. Specifications of Converter Transformers for Kii-
atmospheric conditions were developed for this              Channel HVDC, Phase I
project, which reduced the amount of cooling water             Capacity      Anan converter station   Kihoku converter station
needed.
                                                             Capacity                  872 MW/436 MW/436 MW

                                                             Voltage                     500 kV/110 kV/110 kV
CONVERTER TRANSFORMER
    Converter transformers for the two converter             Impedance                            16%

stations, the Anan converter station and the Kihoku          Connection                         YNy0d1
converter station, were also supplied. The                   Audible noise           70 dB                     60 dB
specifications of the transformers are shown in Table
4. Except for the audible-noise level, the electrical
performance of the two transformers is the same. In
12-pulse conventional converter stations, converter
transformers are arranged separately in a 6-pulse
configuration; in the Kii-Channel HVDC system, each
converter transformer has triple coils for two DC
terminals (see Fig. 7).
    For the Kihoku converter station, a structure with
three sets of single-phase 4-legged coils was used
because of the transportation restraints. The 4-legged
coils are arranged in a 6-pulse operation on each main
core. For the Anan converter station, six sets of single-
phase center cores were used because of the weight
limitations.
    Before manufacturing the converter transformers,
several tests were carried out using a prototype model.     Fig. 7— 872-MVA Converter Transformer (Kihoku Converter
To evaluate the insulation, the DC dielectric materials     Station).
were tested for one year. With the help of computer         The size was reduced by using triple coils for two DC terminals.
simulation using a DC electric field, a number of
characteristics of insulators were analyzed and highly
reliable converter transformers were manufactured.
Some specific problems of converter transformers,           system and converter control system for both the
such as magnetization loss, audible noise, and              converter stations and for the substation control system
conducting loss caused by harmonic currents, were           for the Kihoku converter station (see Fig. 9).
investigated by using computer simulation.                  (1) Supervisory substation control for the human
                                                            interface and monitoring
CONTROL AND PROTECTION PANELS                                   Because the HVDC system consists of many pieces
    HVDC control and protection panels are important        of equipment, there was a strong need for a system
for HVDC systems. The performance and reliability           that would assist in human operation and monitoring
of the Kii-Channel HVDC system should be especially         of the system. A high-speed analyzing system was
high because it is a bulk transmission system. The          introduced to look for defects in the HVDC system; it
configuration of the control system for the Kii-Channel     analyzes waveforms and generates a transient analysis
HVDC system is shown in Fig. 8. It has the following        of the system faults.
features;                                                   (2) HVDC master control for system control and
(1) supervisory substation control for the human            protection
interface and monitoring;                                       The HVDC master control system consists of a
(2) HVDC master control for system control and              power-system controller and a converter-station
protection;                                                 controller. The power-system controller enables the
(3) converter control for the converter-unit sequence       power system to be stable and ensures continuous DC
and converter-triggering pulse generation.                  operation during AC faults and power modulation. The
    Hitachi is responsible for the HVDC master control      converter-station controller enables power sharing
                                                                                                          Hitachi Review Vol. 50 (2001), No. 3   119


                                                      Signal                    Signal
                                                      transmission              transmission
       Anan converter station                         system                    system                        Kihoku converter station

                                             Pole I                                      Pole I
                                             converter               Pole I              converter
                                             control                                     control
       Supervisory         Operation                                                                       Operation         Supervisory
       control             control                                                                         control           control
                                             Pole II                                     Pole II
                                             converter               Pole II             converter
                                             control                                     control

           Master converter                           Signal                    Signal
           station can be                             transmission              transmission
           switched according                         system                    system
           to operation.



            Thyristor valve                       Converter Control System                Operation Control System        Supervisory Control

               • Thyristor              • DC voltage control          • Cooperative       • Power distribution             • System operation
                 trigger-pulse          • DC current control            control with        control                        • State monitoring
                 generation             • Start and stop control        opposite
                                        • Pulse phase control           terminal
                                                                                                                         • High-speed waveform
                                                                                                                           monitoring equipment
                                       • Continuous operation                              • AC system stabilizing       • Simulator for training
                                         during AC system                                    control                       and analysis
                                         fault
                                                                                          • Power disturbance
                                                                                            damping control (SSR)
                                                                                          • Generator cooperative
                                                                                            control

    SSR: supplemental subsynchronous regulation

Fig. 8— Configuration of Control & Protection System for the Kii-Channel HVDC.
Reliability was improved by installing dual operation control system at both the converter stations and
master/slave switching. Dual systems were introduced to further improve reliability.




                                                                               (3) Converter control for the converter-unit sequence
                                                                               and converter-triggering pulse generation
                                                                                   A converter-triggering pulse is generated by the
                                                                               firing of a thyristor valve in accordance with the power
                                                                               reference from the HVDC master control system.
                                                                               Regarding the hardware, Hitachi’s MPU “SH3,” which
                                                                               is highly effective in high-speed sampling and
                                                                               calculations, satisfies the system requirements.

                                                                               CONCLUSIONS
                                                                                  In this paper, we described the work, technologies,
                                                                               and products of the largest HVDC system in Japan,
Fig. 9— Substation Control System of the Kihoku Converter                      the Kii-Channel HVDC project, which has been in
Station.                                                                       commercial operation since June, 2000.
                                                                                  The research and experience we have had in the
                                                                               planning and construction of the Kii-Channel system
between the poles, quick recovery from DC-system                               should be applicable to the construction of power
faults, and over-load operation during power-system                            systems in the future.
emergencies.
                                                                      The 1,400-MW Kii-Channel HVDC System        120

ABOUT THE AUTHORS

         Hiroyuki Nakao                                           Hiroaki Miyata
         Joined the Kansai Electric Power Co., Inc. in 1974,      Joined Hitachi, Ltd. in 1994, and now works at the
         and now works at the Kii Converter Station. He is        Power Electronics Devices & Systems Division,
         currently engaged in the development of new              Power & Industrial Systems. He worked in thyristor-
         technologies for trunk-line substations and in design    valve design for the Kii-channel HVDC system, and
         and construction management, and at the Kii-channel      is currently engaged in the design of power
         HVDC system, is involved in system design and the        electronics equipment for power systems. Mr. Miyata
         development of DC facilities. Mr. Nakao is a member      is a member of IEEJ, and can be reached by e-mail at
         of IEEJ, and can be reached by e-mail at                 hiroaki_miyata@pis.hitachi.co.jp.
         k558857@kepco.co.jp.
                                                                  Makoto Kadowaki
         Masahiro Hirose                                          Joined Hitachi, Ltd. in 1993, and now works at the
         Joined Shikoku Electric Power Co., Inc. in 1985, and     Power and Industrial Systems Division, Power &
         now works at the Power System Engineering Dept.          Industrial Systems. He is currently engaged in the
         He is currently engaged in the design and                design and ultra-high voltage and capacity
         construction of substation facilities, and at the Kii-   transformers. Mr. Kadowaki is a member of IEEJ,
         channel HVDC system, is involved in device design.       and can be reached by e-mail at
         Mr. Hirose can be reached by e-mail at                   makoto_kadowaki@pis.hitachi.co.jp.
         hirose12293@yonden.co.jp.
                                                                  Takahiro Oomori
         Takehisa Sakai                                           Joined Hitachi, Ltd. in 1993, and now works at the
         Joined Electric Power Development Co., Ltd. in           Power and Industrial Systems Division, Power &
         1973, and now works at the Substation & HVDC             Industrial Systems. He worked in the design of the
         Technology Group, Engineering Division. He is            Kii-channel HVDC system, and is currently engaged
         currently engaged in the design and construction of      in the design of control and protection equipment in
         substations and converter stations, and at the Kii-      power systems. Mr. Oomori is a member of IEEJ, and
         channel HVDC system, is involved in system design        can be reached by e-mail at
         and the development of DC facilities. Mr. Sakai is a     takahiro_oomori@pis.hitachi.co.jp.
         member of IEEJ, and can be reached by e-mail at
         takehisa_sakai@epdc.co.jp.                               Akihiko Watanabe
                                                                  Joined Hitachi, Ltd. in 1992, and now works at the
         Naoki Kawamura                                           Power and Industrial Systems Division, Power &
         Joined Hitachi, Ltd. in 1989, and now works at the       Industrial Systems. He is currently engaged in the
         Power and Industrial Systems Division, Power &           design of monitoring and control systems. Mr.
         Industrial Systems. He worked in the design of the       Watanabe is a member of IEEJ, and can be reached
         Kii-channel HVDC system, and is currently engaged        by e-mail at akihiko_watanabe@pis.hitachi.co.jp.
         in the design and development of monitoring and
         control equipment for power system. Mr. Kawamura
         is a member of IEEJ, and can be reached by e-mail at
         naoki_kawamura@pis.hitachi.co.jp.

				
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